This invention relates in general to noise responsive devices and in particular to an electronic circuit for automatically adjusting the volume of an audio program in response to the level of ambient noise.
Oftentimes, an audio program, such as the audio output of a radio, tape recorder, television, and the like, is heard by a listener in an environment which includes a certain amount of ambient or background noise. The amount of such ambient noise is rarely constant, but rather varies considerably in relation to the relatively constant volume of the audio program. Many devices are known in the art for automatically adjusting the volume of an audio program to compensate for variations in the level of the ambient noise. Typically, these devices sense the magnitude of the ambient noise, using a microphone or similar means, and automatically increase or decrease the volume of the audio program in accordance with changes in such magnitude. Unfortunately, known automatic volume control devices are typically complicated in structure and, as a result, rather expensive. Thus, it would be desirable to provide an automatic volume control circuit for an audio program which is simple and inexpensive in construction and operation.